Kathrine Switzer in London for this year’s race.
Photograph: NurPhoto/NurPhoto via Getty Images

There are many differences between Sunday’s London marathon and the one run in Boston, Massachusetts last Monday, not least the weather.

While Boston’s runners struggled in wintry conditions, London’s race is predicted to be the hottest since the event began in 1981. Hopes that the Kenyan favourite, Eliud Kipchoge, could break the world record if he wins a third London marathon now look a little on the optimistic side.

But perhaps the most symbolic difference between the two races is also the most subtle. There was no runner wearing No 261 at Boston on Monday. The reason? Ask the person wearing that number at London.

For it was Switzer who in 1967 became the first woman to run Boston as a registered entrant. It seems extraordinary today, but 50 years ago women were not allowed to compete in the world’s oldest annual marathon.

True, some had run the race unofficially before, but Switzer’s participation was to change everything, even if she did not realise its significance when, wearing an official bib, No 261, she lined up surrounded by hundreds of men for the start of the race.

“I had no intention of making history that day,” she said. “I was a kid who wanted to run. I signed up to the race. I signed my name K Switzer – I’d done it since I was 12 – and they thought I was a guy. I wasn’t trying to defraud them but my coach insisted that I officially sign up. He said: ‘You don’t mess around with Boston, you don’t just jump in the race.’ Other women had run marathons, and even one at Boston the year before, but not officially. We checked the rule book. Nothing in the rule book about it being for men only. It was only a tradition. They just assumed a woman couldn’t or wouldn’t want to run. Even on the entry form there was nothing about gender.”

What happened next has entered the annals of marathon history. Four miles into the race, an official, Jock Semple, attempted to grab Switzer, yelling, “get the hell out of my race and give me those numbers”.

Jock Semple tries to throw Kathrine Switzer out of the 1967 Boston marathon. Tom Miller, right, in bib No 390, is about to intervene. Photograph: Bettmann/Bettmann Archive

Switzer remembers the moment graphically. “My coach was screaming at him, saying ‘She’s OK, leave her alone, I’ve trained her’, but he [Semple] was tired, and he was a man of his time. He didn’t think women should be there.”

Switzer’s boyfriend Tom Miller, a 17-stone ex-All American football player, who was also running the race, bodychecked Semple, knocking him into the air, a moment caught in photographs that went around the world. Switzer went on to finish in 4 hours 20 minutes, almost an hour after the first unregistered woman to finish, Bobbi Gibb.

Official retribution was swift. “In the end, after I’d finished the race, I was disqualified and expelled from the athletics federation because I had run with men, because I had run more than a mile and a half and because I had fraudulently entered the race, which was not true – and the worst one was because I had run without a chaperone. It just shows the attitude that existed in 1967: people thought that if women ran they would turn into a man or that it was socially objectionable.”

Her actions triggered a clamour for equality in the running world that could not be silenced. Five years later, Boston allowed women to compete and Switzer was on her way to becoming a de facto ambassador for women’s running. On Sunday she will be the official starter for the women’s elite race, after which she will join around 40,000 people looking to get around the 26.2 mile course in temperatures that experts warn will prove difficult for the non-elite runners.

“Take every opportunity to consume fluids,” said Andrew Jones, professor of applied physiology at Exeter University. “If there’s shade on the course, use that. Prepare yourself mentally. It’s going to be a bit of a slog over those last few miles.”

Switzer, though, is not deterred by the conditions. “I’ve wanted to run this race since it first started. I’m delighted to be here on the 100th anniversary of women’s right to vote.”

London is close to her heart. She competed in an all-women marathon in the capital in 1980, an event sponsored by the Avon cosmetics company that played a pivotal role in bringing gender equality to running. “That race got the women’s marathon into the Olympic games. That was a huge battle for women’s equality. To me, it was the physical equivalent of the right to vote. That was about intellectual, social acceptance; this was the physical acceptance. That was amazing.”

Last year, half a century on from the infamous race that earned her global recognition, Boston retired bib No 261 as a mark of respect to Switzer, for whom running has always been gender blind. “It’s about equality, it’s about inclusion and it’s also about peace,” she says.